Excerpt: The History of the World According to Incubi

The history of the World According to Incubi
Dwarves
Dwarves are a case commonly used by the Imperium to justify the reason that mixing relationships between mortcayads and any magical creature should be banned. Dwarves lost their magic, and their unique appearance.
The composition of dwarves explains why this is even more extraordinary than to be expected. Dwarves are creatures that do not hold themselves to the traditional sexes. The reason most other races assumed dwarves were only male was the fact that they all had beards.
While in fact dwarves were actually sexless. They were creatures that were only a specified gender when it became necessary to procreate. Then one of a pair would choose to be the carrier and the other of the pair would choose to be the planter.
Due to this nature in dwarves they were very indiscriminate in choosing both a partner and a background for said partner. Dwarves were interbreeding when it was not something done by any group (see Therian separation).
The imperium though hand a hand in keeping dwarves once they had intermingled enough to become indistinguishable from mortcayad groups. THey did not want dwarves to rise again as yet another group that questioned their power and felt no need to proclaim loyalty to the Imperium.
The Therians had done it, the Incubi had done it but it was the dwarves that concerned the Imperium. Why? Because they were the creatures most likely to take up a cause. The therians were not interested if you were not a therian and the incubi were so long lived that they could not be concerned with day to day rulers.